Bring stout and butter to simmer in large saucepan over medium heat, stirring to melt butter. Add cocoa; whisk until mixture is smooth. Cool slightly.

Beat eggs and sour cream in large mixing bowl fitted with paddle attachment. Add chocolate mixture and beat until just combined. Sift in flour, sugar, baking soda and salt. Beat to blend. Divide batter among pans. (I had enough batter left over for and additional 36 mini cupcakes).